The commercially available alpha-amylase from Aspergillus oryzae which is widely used as a baking additive was compared with a highly purified enzyme preparation. We used enzyme allergosorbent test (EAST), EAST inhibition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focussing, immunoblotting, and N-terminal amino acid sequencing to characterize the causative allergen. Our screening comprised 89 partially selected bakers. Forty-three (48%) of them had work-related respiratory symptoms; 14 (32%) of whom were sensitized to the baking additive. Significant immunological differences could not be found between crude and purified sample with the exception that the latter one produced nearly twice as high antibody values. Iodine starch staining demonstrated that the component which was exclusively or predominantly bound by IgE antibodies of symptomatic bakers represents the active alpha-amylase. According to the International Union of Immunological Societies (IUIS) nomenclature, the term Asp o II is suggested for this important occupational allergen.